A light-emitting diode (LED) has drawn attention as a backlight (light source) for a liquid crystal display and the like, or as a light source for an illuminator that is alternative to an incandescent lamp and a fluorescent lamp.
Typically, an LED chip that is mounted on a substrate and the like is sealed with a sealant (sealing lens). This sealant uses silicon and the like as a main constituent material, and has a refractive index in the order of about 1.5. When light is incident from a material with the refractive index of 1.5 toward the air with the refractive index of 1.0, a critical angle may become about 41.8 degrees, and any light with an angle of incidence onto the front face of the sealing lens that exceeds 41.8 degrees may be totally reflected, resulting in preventing such light from being emitted externally. Further, for a light source using the LED, it is possible to obtain light with the wavelength different from that of light emitted by the LED in a manner of kneading a fluorescent material into the sealant. The fluorescent material that is kneaded into the sealant is excited by light irradiated by the LED to emit light almost uniformly in all directions. This shows that the light extraction efficiency is improved by allowing the sealing lens to have the shape that causes the largest amount of light emitted within the sealing lens to directly pass through the front face of the lens, that is, to have the hemispheric shape.
As a method of forming a sealing lens in the hemispheric shape, a resin sealing method for an LED chip has been disclosed that provides a resist layer at the outside of a sealing region to adjust a lens shape on the basis of a difference in the water-repellent property between the resist layer and a substrate (for example, see Patent Literature 1).